In a prior art apparatus for controlling the direction of irradiation of the headlights, a brushless motor is used as a driving force for moving the direction of the irradiation, wherein an output shaft of the apparatus operatively connected to the headlights is connected to the brushless motor over a speed reduction mechanism.
In such a prior art apparatus using the brushless motor, it is, however, disadvantageous in that a position sensor for detecting rotational positions of the motor is necessary and therefore such apparatus is high in its manufacturing cost and more complicated in its structure. Furthermore, when a potentiometer is used as the position sensor, the detection of the position is less accurate and less reliable because the position of the motor shaft is detected by its contact resistance. It is accordingly proposed in the prior art that a stepping motor, a rotational position of which is controlled by a number of stepping pulses, is used instead of the brushless motor as the driving force for the headlights.
Even in the case that the stepping motor is used, detected positions of the motor inevitably include detection errors due to various causes. For example, in a case that a magnetic sensor is used for detecting the rotational positions of an output shaft of the apparatus, the detected positions include errors caused by the variations of magnetic fluxes of permanent magnets when the temperature changes. Furthermore, the detected positions may include errors caused by stopping deviation, errors caused by abrasion in response to its number of use, and errors caused by bounds at impingement of the output shaft during an initialization process.
As above, the detected positions have a certain range, during which the detected amount from the sensor would not be changed even when the output shaft of the apparatus is rotated. Therefore, it may not be possible in some cases that the rotational positions of the output shaft will be accurately detected. For example, in case that the stepping motor is out of order due to a disconnection of an electric power line or operated with lost motion, the output shaft will not be rotated in proportion to the stepping pulses. Since the detected voltage from sensors has a certain range during which the detected voltage remains unchanged, it may not be possible in some cases whether the stepping motor is in a good operational order or not when the motor should be rotated within a small rotational angle.